Pen type drug delivery devices have application where regular injection by persons without formal medical training occurs. This may be increasingly common among patients having diabetes where self-treatment enables such patients to conduct effective management of their disease.
There are basically two types of pen type delivery devices that allow a user set to a variable dose of medication: resettable devices (i.e., reusable) and non-resettable (i.e., disposable). These types of pen delivery devices (so named because they often resemble an enlarged fountain pen) are generally comprised of three primary elements: (i) a cartridge section that includes a cartridge often contained within a housing or holder; (ii) a needle assembly connected to one end of the cartridge section; and (iii) a dosing section connected to the other end of the cartridge section. A cartridge (often referred to as an ampoule) typically includes a reservoir that is filled with a medication (e.g., insulin), a movable rubber type bung or stopper located at one end of the cartridge reservoir, and a top having a pierceable rubber seal located at the other, often necked-down, end. A crimped annular metal band is typically used to hold the rubber seal in place. While the cartridge housing may be typically made of plastic, cartridge reservoirs have historically been made of glass.
The needle assembly is typically a replaceable double-ended needle assembly. Before an injection, a replaceable double-ended needle assembly is attached to one end of the cartridge assembly, a dose is set, and then a dose is administered. Such removable needle assemblies may be threaded onto, or pushed (i.e., snapped) onto the pierceable seal end of the cartridge assembly.
The dosing section or dose setting mechanism is typically the portion of the pen device that is used to set a dose. During an injection, a spindle contained within the dose setting mechanism presses against the bung or stopper of the cartridge. This force causes the medication contained within the cartridge to be injected through an attached needle assembly. After an injection, as generally recommended by most drug delivery device and/or needle assembly manufacturers and suppliers, the needle assembly is removed and discarded.
Different types of pen delivery devices, including disposable (i.e., non-resettable) and reusable (i.e., resettable) varieties, have evolved over the years. For example, disposable pen delivery devices are supplied as self-contained devices. Such self-contained devices do not have removable pre-filled cartridges. Rather, the pre-filled cartridges may not be removed and replaced from these devices without destroying the device itself. Consequently, such disposable devices need not have a resettable dose setting mechanism.
In contrast to typical disposable pen type devices, typical reusable pen delivery devices feature essentially two main reusable components: a cartridge holder and a dose setting mechanism. After a cartridge is inserted into the cartridge holder, this cartridge holder is attached to the dose setting mechanism. The user uses the dose setting mechanism to select a dose. Before the user injects the set dose, a replaceable double-ended needle assembly is attached to the cartridge housing.
This needle assembly may be threaded onto or pushed onto (i.e., snapped onto) a distal end of the cartridge housing. In this manner, a double ended needle mounted on the needle assembly penetrated through a pierceable seal at a distal end of the cartridge. After an injection, the needle assembly is removed and discarded. After the insulin in the cartridge has been exhausted, the user detaches the cartridge housing from the dose setting mechanism. The user can then remove the empty cartridge from the cartridge retainer and replace the empty cartridge with a new (filled) cartridge.
In certain typical a variable dose drug delivery devices such as those described above, a dial sleeve is engaged with the housing of the device via a helical groove. Typically, this dial sleeve is rotated out away from the housing on a helical path to allow the user to set a variable dose of medication. This dial sleeve spins back or rotates back towards the housing when the set dose is delivered.
This helical thread may have one or more radial stop faces that engage when the dial sleeve has been dialled up to a certain non-variable maximum dose. For example, in certain typical drug delivery devices used for the administration of insulin, such a non-variable maximum dose may be on the order of 50-80 International Units (IU). In this manner, a user is prevented from dialing up a dose greater than this non-variable maximum dose. In certain known devices, these stop faces can be molded into the plastic components as fixed stop faces. These stop faces may or may not be part of the helical thread form.
Known dose setting mechanisms that do not allow for varying such a maximum dose setting have certain perceived disadvantages. For example, a drug delivery device having a non-variable maximum dose stop does not enable a user or healthcare professional to limit the maximum dose that can be dialled on a variable dose pen. Therefore, one disadvantage of this arrangement is that it tends to increase the risk of a potential dose error. In addition, such an arrangement makes the device more difficult to set in low light conditions or for users having poor vision.
Another disadvantage of drug delivery devices having a fixed maximum dose is that a parent or a care giver cannot limit the maximum dose that can be delivered from a device. Consequently, such a device may pose certain safety issues when used by a child or elderly patient without supervision.
There is, therefore, a general need for an adjustable maximum dose stop that enables a user or healthcare professional to limit the maximum dose that can be dialed on a variable dose pen. A drug delivery device that utilizes an adjustable maximum dose would offer a number of advantages. As one example, a user can pre-set the maximum dose of the drug delivery device to be a certain regular daily dose and thereby reduce the risk of a potential dose error. In addition, an adjustable maximum dose stop makes the drug delivery device easier to set in low light conditions or for users having poor vision. For example, with such an arrangement, the user simply dials the dose dial grip until the maximum dose stop engages and then delivers the dose. In addition, such an adjustable maximum dose stop allows a healthcare professional to limit or set the dose for the patient who has poor dexterity, poor vision or limited understanding of variable dose pen types.
It is, therefore, the object of the present invention to take these disadvantages associated with issues into consideration in the design and development of drug delivery devices.